The Louisville Ridge, a hotspot chain, obliquely subducts at the Tonga-Kermadec consuming plate boundary (Southwest Pacific). This ridge has swept the Tonga Trench and the ridge-trench junction point is rapidly (at least 10 cm per year) migrating southward along the Kermadec trench. Results from a comparative morphological study between the Kermadec and Tonga margins, and from the Seapso 5 seabeam survey around the ridge-trench junction consider the effects of the subduction of an oblique ridge on an active margin. Underplating of material scraped and pushed in the front of the ridge could be responsible for the high-standing position of the Tonga platform in the prolongation of the Kermadec active volcanic line.